React 0.12 support

Provide React 0.12 support in all react-bootstrap components.

BREAKING CHANGES:
It's no longer possible to use key indiscriminately within React components, so I had to make the following changes to component props:

Panel: key -> selectKey
MenuItem: key -> selectKey
NavItem: key -> selectKey
TabPane: key -> selectKey
ListGroupItem: key -> clickKey (named this 1 click because it's used in the onClick handler, while all the others are used in onSelect handlers)

Comments or help finishing this off is welcome.
the reason for including them is for the build stage (amd dislikes requiring from react/lib). For addon utilities you do not want to rely on your consumer using addons, also there are really annoying bugs when requiring react & react/addons in the same project. Inlining these utilities has become the defacto standard for larger react libs, until they release addons seperatly

as an addendum tho Pete hunt does have an npm package `react-classset` and I got tired of c/p `cloneWithProps` everywhere so released `react-clonewithprops`. either or one of these might be a good alternative to inlining more utils